This invention relates to tractor-trailers and more particularly, to trailers that include a hill start assist function.
Tractor-type trucks are designed to tow trailers and semi-trailers having large loads. The loads may include goods, supplies or other freight. Some tractor trucks include an automated manual type transmission. This type of transmission presents a challenge to operators of the trucks when the truck has to accelerate from a stationary position on an incline.
In order to stop or maintain a stationary position (at a traffic light for example), the brakes are applied. When the truck has to accelerate from this position, the operator has to shift his or her foot from the brake pedal to the accelerator pedal. However, during this transition period, the truck has a tendency to roll back (if moving forward) as a result of the brakes being released since the driveline does not become engaged instantly upon a depression of the accelerator pedal. This rollback may be due to the incline (or grade) of the road, the load or weight of the truck or a combination thereof.
Hill start assist systems have been developed to prevent rolling back of the vehicle during the transition period. The present systems, however, do not provide adequate protection against the rolling back of a truck. Some systems only use brakes of the tractor portion of the truck to keep the truck from moving or rolling back. These systems do not use trailer brakes to assist in holding the truck in a stationary position on an incline. The brakes of the tractor may not be able or adequate to hold the tractor trailer combination on the grade. The brakes of the tractor may also wear out faster in these systems. In some situations (e.g. particular inclines), the present systems also do not keep even a tractor (without an attached trailer) from rolling back during this transition.
What is desired, therefore, is a hill start assist system that provides adequate protection against the rolling back of a truck that is transitioning from a stationary position.